The Institute of Electrical and Electronics Engineers (Institute of Electrical and Electronics Engineers, IEEE) 802.11 standards organization plans to formulate an Internet of Things standard based on Wireless Fidelity (Wireless Fidelity, Wi-Fi), with an objective to promote application of the Wi-Fi technology to the Internet of Things field, wearable electronic devices, and digital medical devices. A Wi-Fi communications module of an existing wearable electronic device has excessively large power consumption, and cannot be directly applied to a wearable electronic device. To apply the Wi-Fi technology to the Internet of Things field and the wearable electronic devices, reducing power consumption of the Wi-Fi communications technology is very necessary.
To resolve the foregoing problem, the IEEE 802.11 standards organization proposes a wake-up radio/receiver (Wake-Up Radio/Receiver, WUR) technology with ultra-low power consumption. A WUR can be used to reduce average power consumption of the Wi-Fi communications technology, and also implement on-demand (On-Demand) real-time data transmission. According to the WUR, a radio/receiver interface with ultra-low power consumption is added to a Wi-Fi device of a device. When no data is received or transmitted, a main communications module (for example, a Wi-Fi module) of the device enters deep sleep, and the WUR module is started to perform listening with ultra-low power consumption. For example, as shown in FIG. 1, when an access point (Access Point, AP) needs to transmit data to a station (Station, STA), the AP is a wake-up device, and the STA is a waked-up device. The AP first sends a wake-up packet (Wake-Up Packet, WUP) to a WUR module of the STA. After receiving the wake-up packet, the WUR module of the STA checks a receiver address of the wake-up packet and confirms correctness and authenticity of the wake-up packet. If the receiver address of the wake-up packet matches an address of the WUR of the STA, and the wake-up packet is correct and authentic, the WUR module of the STA sends a wake-up signal to a main communications module (for example, a module) of the STA, to wake up the main communications module of the STA. After sending the wake-up signal, the WUR module of the STA may enter a deep sleep state (a state in which power consumption is close to 0). To further reduce average power consumption of the WUR, the WUR may start duty-cycling (Duty-Cycling), that is, the WUR periodically “wakes up and sleeps”. In the prior art, a “synchronous wake-up” mechanism is used, that is, a second device stays time-synchronized with a WUR of a first device, and the second device can accurately find a location, on a time axis, of a wake window (Wake window) of the WUR of the first device. As shown in FIG. 2, a period of a WUR of a waked-up device is 100 milliseconds (ins), and a wake window length W is 2 milliseconds (ms). When a wake-up device needs to send data to the waked-up device, the wake-up device sends a wake-up packet (WUP) to the WUR of the waked-up device in a wake window of the WUR of the waked-up device, to wake up a main communications module of the waked-up device.
In the foregoing “synchronous wake-up” mechanism, the wake-up device needs to periodically send WUR time synchronization frames. As a result, energy overheads are relatively large, and electric energy of the wake-up device is greatly wasted. In addition, as shown in FIG. 3, when a waked-up device is connected to a plurality of different wake-up devices, for example, the waked-up device is connected to a wake-up device 1, a wake-up device 2, and a wake-up device 3, and the plurality of wake-up devices belong to different basic service sets (Basic Service Set, BBS) or belong to different networks, if the “synchronous wake-up” mechanism is used, a WUR of the waked-up device needs to maintain a plurality of pieces of clock information, and needs to periodically receive time synchronization frames from the plurality of wake-up devices. This significantly increases complexity and power consumption of the WUR module of the waked-up device, and reduces a standby time of a battery of the waked-up device. In addition, the plurality of wake-up devices separately send the time synchronization frames, thereby wasting a large quantity of air-interface time-frequency resources.